IMO, miles are not an appreciating asset and should be used whenever convienent. I do agree with these other posters that one should use them in a wise manner to maximize value. For instance, in the last year I burned 82,500 upgrading my and my parents tickets to HNL, which I thought was a great value. I also bought a domestic reward (the horror!) with the old 11 hour advance purchase saving 800 bucks.

I think the key is to learn as much about the program and redemption as you can to further maximize your value. For instance, I booked (but later cancelled) a coach ticket with a stopover in Tokyo to Singapore open jaw to Bangkok. For 60K miles, one can book at a ticket that sees many of the highlights of asia...